1. Field of the Invention
This invention relates to a gas laser oscillator, and particularly relates to a laser oscillator designed to elongate the service life of the ion laser tube.
2. Description of the Prior Art
A conventional gas laser oscillator comprises an ion laser tube provided with a capillary tube and a cathode and an anode as discharging electrodes, electromagnets for plasma focusing arranged around the ion laser tube, and a pair of mirrors for optical resonance at the both ends of the ion laser tube. Application of voltage from the power supply across the cathode and the anode causes plasma discharge. The direct current voltage has been already applied to the electromagnets for plasma focusing. The magnetic field given by the plasma focusing magnets works so that the plasma generated between the cathode and the anode is focused. When the ion laser tube discharges, the mirrors at the both ends cause optical resonance and the laser beam is obtained.
Since conventional gas laser oscillators as described above are designed considering the magnetic field strength at the capillary tube in the ion laser tube only, the cathode end face also has a considerably high magnetic field strength. Usually, the capillary tube is subjected to the magnetic field of about 1,000 gauss and the magnetic field strength near the cathode end face is about 500 to 800 gauss. For this reason, plasma tends to concentrate to a certain limited part on the cathode, which deteriorates the cathode resulting in shorter service life of the ion laser tube.
Besides, since the diameter of the lines of the magnetic flux covering the cathode end face becomes larger than the diameter of the capillary tube at the end of the capillary tube, the plasma does not sufficiently focus at the end of the capillary tube. This causes plasma crushing at the capillary tube end involving extremely high temperature, resulting in evaporation at the end face of the capillary tube (sputtering). As a result, substances separated from the end face of the capillary tube due to evaporation make the Brewster windows on the cathode side and the anode side dirty and confine the argon gas (gas laser medium in the ion laser tube) leading to gas consumption, which reduces the service life of the ion laser tube.